Polymerization of conjugated diene hydrocarbons



Patented Sept. 18, 1945 roimmnrza'non F CONJUGATED mama maocaanoss George Browning, In, Akron, Ohio, assignor, by mesne assignments, to The B. F. Goodrich Company, Akron, Ohio,- a corporation of New York' No Drawing. Application February 7, 1941, Serial N0. 377,837

This invention relates to the polymerizationoi conjugated diene hydrocarbons and particularly to a method whereby conjugated diene hydro-' carbons may be polymerized in an aqueous emul-v sion to form products closely resembling natural crude rubber. Y

The emulsion polymerization of conjugated diene hydrocarbons either alone or in admixture with other coniugated j'dienes" or vinyl-type comononiers to form compositions bi matter more or less resembling rubber is well nmwm It has 9Claims. (Cuzco-424.5)-

merization in aqueous emulsion at 30 C. of 75 parts by weight of butadiene and 25 parts of acrylonitrile. In the presence of .31 parts of tetramethyl thiuram disulfide, it took 153 hours -to complet the polymerization. In the presencebeen .commonlyobservediho'iv ever, that the prod ucts oi'such' polymerization oitenresemble vul-- in respect to solubility. plasticity. 1:

- canized rubber rather than naturaicruderubber characteristics; Thus, it has; erzehheen- "found that the were insoluhle iiiand, in some cases',--n'ct even-swelled by smear acetone,

and that they were non-plastic materials which either would'nothomogenise on'afmill or which were-very 'diificult to mill and to subject to other-ordinary processing operations i or natural rubber.

I have now discovered that the tetra-allryl thiuram sulfides in which the four alkyl groups contain atotal '01 at least 12 carbon" atoms modify the emulsion polymerization oi conjugated dienes in such a manner that polymers more nearly resembling natural crude rubber are produced than when the polymerization is carried on in the absence of the materials 01' this invention. The action oi these materials is surprising because the thiuram sulfides are accelerators oi vulcanization, and many accelerators strongly inhibit the polymerization oi conjugated dienes. Furthermore, the lower tetra-alwl thiuram sulfides such as tetramethyi and tetraetbyl thiuram monoand disulfide inhibit the polymerization of conjugated diene' hydrocarbons. The tetraisopropyl sulfides do not inhibit emulsion polymerization, however, and certain of the higher thiuram sulfides such as tetrabutyl thiuram disulfide accelerate the polymerization somewhat. Other materials which may be em-' ployed to modiiy polymerizations in accordance with the method of this invention include tetrapropyl thiuram monosulfide, tetrapropyl thiuram disulfide, tetra-act. amyl thiuram disulfide and mixed thiurams such as dipropyl dibutyl thiuram disulfide and diethyl dibutyl thiuram inonosulfide.

The term sulfide as used herein signifies both 015484 parts 0! tetrapropyl' thiuram disulfide, however, the polymerization-was complete in hours, and in the presence of 1.01 parts of tetrabutyl thiurarn disulfide, the polymerization' was complete in 40 hours. The synthetic rubbers obtained by the coagulation of the latices obtained as products of the above polymerizations in the presence of thiuram disulfides were coherent, plastic materials having a, much greater-solu-f bility in benzene than a polymer prepared in theabsence of any 'modifler,'and the vulcanizates prepared from the modified polymers exhibited j an increased elongation. Similar results'are observed when the thiu'ram sulfides of this invention are employed'duririg' the emulsion copoly merization of butadiene and methyl methacrylate.

While the above example is confined to the use 01 disulfides as modifiers, it will be clear to those skilled in the art thatother polysulfides such as the corresponding triand tetrasulfides and the mono-sulfides may similarly be employed.

-The proportion in which the modifier is included afiect the nature oi the polymer produced, and

amounts up to 6% or over may advantageously be employed. c

Although the exact manner in which the modifiers 01 this invention function is not understood,

it is believed irom the nature of the changes in properties eilected by polymerizing monomers in the presence of modifying agents that these materials in some way inhibit the formation of cross-linkages but still permit the formation oi long, straight chains of the polymerizable mono mers, It is believed that in the-absence of some agent which serves to prevent or inhibit crosslinkage, the products of. emulsion polymerizations which-have been carried to completion contain numenous cross-linkages which affect the properties ,of the polymer in much the same manner as the cross-linkages iormed during the wilcanization of natural crude rubber with the aidoi' sulfur change the properties of the crude rubber.

"polymeric chains only by 2 This theory explains why the polymers prepared in the presence of modifying agents are in general more plastic and more soluble than unmodified polymers. This theory is presented only by way of explanation and is not intended as a limitation on the invention, for regardless of the correctness of the theory, the inclusion in emulsion polymerization batches of a tetra-alkyl thiuram sulfide in which the alkyl groups contain a total of. at .least 12 carbon atoms produces the beneficial results heretofore described. Y

The modifying agents of this invention may be employed in the polymerization in aqueous emulsion of conjugated butadiene hydrocarbons such as butadiene (butadiene-1,3), 2,3-dimethylbutadiene, lsoprene, or piperylene either alone or in admixture with each other or with monomers copolymerizable therewith. A number of materials which contain the group initiators of. polymerization such as per-compounds including hydrogen peroxide, ammonium persulfate, potassium per-sulfate, and other. peracids, peroxides, and per-salts such as persulfates, perborates, percarbonates, and the like, as well as other types of initiators such as diazoaminobenzene, and dipotassium diazomethane disulfonate.

Any of the ordinary emulsifying agents such as fatty acid soaps including sodium oleate and vinylidene chloride. 80

and scope of the invention as defined in the appended claims.

I claim:

1. The method which comprises polymerizing a conjugated butadiene hydrocarbon in an aqueous emulsion in the presence of a small amount of a tetra-alkyl thiuram sulfide in which the alkyl groups contain a total of at least 12 carbon atoms.

2. The method which comprises copolymerizing a conjugated butadiene hydrocarbon and a smaller amount 0! a monomer'copolymerizable therewithin an aqueous emulsionin the presence of a-small' amount of a tetra-allqrl thiuram sulfide in whichthealkyl groups contain a total of at least 12 carbon atoms.

3. The method which comprises copolymerizing a conjugated butadiene hydrocarbon and a smaller amount of a monomer copolymerizable therewith which contains a cnptgroup and polymerizes only by 1,2-addition, in

. an aqueous emulsion in the presence of a small amount of a tetra-allryl thiuram disulflde in which the allqrl groups each contain 3 carbon atoms;

4. The method which comprises copolymerizing butadiene and asmaller amount of styrene in an aqueous emulsion in the presence of a tetra-alb'l thiuram sulfide in which the alkyl groups contain a totalof at least 12 carbon atoms.

5. The method which comprises copolymerizing butadiene and a smaller amountof acrylonitrile in an aqueous emulsion in the presence of a tetra-alkyl thiuram sulfide in which the alkyl groups contain a total of at least 12 carbon sodium stearate, hymolal sulfates and sulfonates 5 including sodium lauryl sulfate and sodium isopropyl naphthalene sulfonate, and salts of hymolal organic bases such as the hydrochloride of diethylamlnoethyloleylamide, trirnethylcetylammonium methyl sulfate, etc. may be employed. 55

Although I have herein disclosed speciflic embodiments of my invention, I do not intend to limit the invention solely thereto, or it will be obvious to thoseskilled in the art that many variations and modifications are within the spirit atoms.

6. The method which comprises copolymerizing butadiene and a smaller amount of acrylonltrile in an aqueous emulsion in the presence of.

' tetra-n-propyl thiuram disulfide.

'1. The method which comprises copolymerizing butadiene and a smaller amount of acrylonitrile in an aqueous emulsion in'the presence of tetraisopropyl thiuram disulfide.

8. The method which comprises copolymerizing butadiene and a smaller amount of methyl methacrylate in an aqueous emulsion in the presence of a tetra-alkyl thiuram sulfide in which the alkyl groups contain a total of at least 12 carbon atoms.

9. .Th method which comprises copolymerizing butadiene and a smaller amount of methyl methacrylate in an aqueous emulsion in the presence of a tetra-alkyl thiuram sulfide in which the alkyl groups each contain 3 carbon atoms.

GEORGE L. BROWNING. Ja. 

